Apps developers predict growth in television apps and even apps for connected
cars in the next few years.

If you have a smartphone, you will almost certainly have added a selection of apps to extend its functions. The small computer programs add specific features and the average smartphone user has more 40 of them.

Smartphone applications have been around for a long time. The Lithuanian app store GetJar, for example, was launched in 2004, while US site Handango began even earlier - in 1999 - and now runs the third largest mobile application store, behind Apple and Google.

And yet, the opening of Apple's App Store in 2008 was the first time that many people were exposed to the world of smartphone apps. Apple's success with the App Store spurred other manufacturers to create their own stores. These days all the major operating system manufacturers have app stores. Google followed Apple's lead in October 2008, BlackBerry App World opened in early 2009 and Microsoft's Windows Phone Store came in October 2010.

Apps are big business. More than 30 billion apps have been downloaded from Apple's App Store, while Google's Play store has seen 25 billion downloads. Plenty of those are free apps but people are willing to spend money on apps, too. Whether they want a GPS-powered app to keep track of their exercise, a mobile recipe book complete with a built-in shopping list or just a game like Angry Birds, there is something for everyone.

While many apps are produced by established software developers, there are plenty of new entrants into this business, encouraged by the opportunity to reach a large number of people quickly, easily and relatively cheaply.

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Apps are increasingly expanding beyond smartphones and tablets. A survey by Appcelerator of more than 5,000 developers found that more than 80 per cent felt they would be making apps for televisions by 2015. Three quarters of developers predicted that they would be building apps for connected cars, while 71 per cent saw a move to games consoles in the future and two-thirds expect to be writing apps for Google Glass, the search giants augmented reality glasses.

Next week developers will gather in London for the Apps World conference at Earls Court. Addressing them will be senior figures from big companies including Samsung and Sony, new media fixtures like Facebook and Google, as well as up-and-coming stars of the app world, such as Hailo and Zeebox.

According to Appcelerator, Apple's iOS platform remains the priority for developers, with 85 per cent saying they were interested in making apps for the iPhone and 83 per cent interested in the iPad. Google's Android devices were not far behind, with 76 per cent interest in Android phones and 66 per cent keen to develop for Android tablets.

The availability of apps has now become an important factor to consider when buying a new smartphone. Apple used to enjoy large numbers of exclusive apps but increasingly, after establishing themselves on iOS, developers have created Android versions of their apps.

RIM, the BlackBerry manufacturer, and Microsoft both face a challenge in convincing people to commit to their new operating systems, without having a large store of apps to put in front of them from day one. Maintaining developer interest is vital.

Microsoft, keen to establish Windows 8 as a viable alternative to Apple and Google, still has some work to do to interest developers in its hardware. Just 33 per cent of developers said they were 'very interested' in making apps for Windows 8 tablets.

These things change quickly, of course. A successful launch this autumn for Nokia's new Windows Phone 8-powered Lumia handsets will go a long way to encourage developers to explore the platform and more competition can only be good for customers.

Next week, The Telegraph is publishing a guide to the 500 must-have apps. Our technology writers have gathered apps from a range of categories, including health, sport, culture, travel and photography. The list will be published in two parts, in the Daily Telegraph on Tuesday and Wednesday. Reflecting the fact that so much of this apps boom has been driven by Apple, our Monday supplement will tell you everything you need to know about the iPhone 5.